The present invention relates to polysiloxane-oxyalkylene block copolymers and, in particular, the present invention relates to polysiloxane-oxyalkylene block copolymers which are useful in controlling the cell size and density of a polyurethane foam during the foaming procedure.
Polyurethane foams are formed by reacting a polyisocyanate with a polyol which may be a polyether containing hydroxyl groups or a polyester containing hydroxyl groups in the presence of a blowing agent, a catalyst such as tin catalyst, and a surfactant. When the polyisocyanate reacts with the polyol, heat is generated which evaporates the blowing agent so it passes through the liquid mixture forming bubbles therein. In addition, water may be added to the mixture to react with excess polyisocyanate to generate carbon dioxide which passes through the mixture forming bubbles. If a surfactant is not used in the foaming coposition, then the bubbles simply pass through the liquid mixture without forming a foam.
In the past, many surfactants were used to form a foam from the liquid mixture, as well as to control the size of the bubbles in the foam so that a foam of a desired density was obtained. Preferably, a foam with small bubbles or cells therein of uniform size was desired in that it was the most desirable foam, that is, a foam having a lower density. As the result of research, it was discovered that polysiloxanes having oxyalkylene units in the polymer chain were useful as surfactants in foaming polyurethane foam. In fact, it was discovered that these polysiloxane-oxyalkylene block copolymers were much more efficient surfactants in foaming polyurethane foam, that is, a smaller quantity of these surfactants was used to produce foams of lower density than was possible with other surfactants.
One difficulty with these polysiloxane surfactants was that the oxyalkylene group was attached by a silicon to oxygen to carbon linkage. This linkage proved to be hydrolytically unstable in that as soon as any water came into contact with the surfactant, the silicon to oxygen to carbon linkage would be hydrolyzed, resulting in a polysiloxane polymer which had an unacceptable foaming efficiency for forming polyurethane foams.
It is to be noted that in forming polyurethane foams, rigid foams are formed with closed cells, while in flexible foam most of the cells are desirably open celled. This is desirable in flexible foams in that a large number of closed cells in the foam will impair the breatheability of the foam structure and its ability to return to its original shape after it has been crushed. Thus, it has been found that polysiloxane polymers which do not have oxypropylene moieties attached thereto are unsuitable as foaming agents for flexible foam is one aspect in that most of the cells that are formed are closed cells.
Another disadvantage with the present polysiloxane-oxyalkylene block copolymers that are used as surfactants for polyurethane foams is that they may only be used for flexible or rigid foams and that a common formulation that can be used for both flexible and rigid foams with minor variation of molecular structure has not been as yet discovered.
In order to improve the hydrolytic stability of the available polysiloxane-oxyalkylene block copolymers, there have been proposed polysiloxane-oxyalkylene block copolymers in which there are SiC linkages connecting the silicon to the polyether moiety. The polyether moiety has an unsaturated olefin group attached to it, which group is reacted with a polysiloxane having free hydrogen atoms through an Si--H olefin addition reaction to form the desired compound. However, the disadvantage of this process for producing polysiloxane-oxyalkylene block copolymers with an Si--C linkage is that it is necessary to produce polyethers with an unsaturated moiety attached thereto. This involves reacting an unsaturated acid, such as an alkenoic acid or unsaturated alcohol, with alkylene oxides to produce the unsaturated polyether. Such compounds are only commercially available to companies and firms that produce and manufacture polyethers for their own particular use.
Another disadvantage of this process for forming polyethers with an unsaturated moiety thereon is that it is very difficult to control the number and type of oxyalkylene groups in the polyether chain. There is a much more simple and efficient way to control the type and amount of oxyalkylene groups in the polyether moiety by blending in different types of polyethers. However, this is not possible by the process of the prior art.
Accordingly, it is one object of the present invention to provide a polysiloxane-oxyalkylene block copolymer in which the oxyalkylene moiety is connected to the silicon atom through a silicon-carbon linkage.
It is another object of the present invention to provide a process for producing a polysiloxane-oxyalkylene block copolymer with a silicon-carbon linkage connecting the polysiloxane moiety to the oxyalkylene moiety, which process is more economical and efficient than prior processes.
It is still another object of the present invention to provide a polysiloxane-oxyalkylene block copolymer surfactant for polyurethane foams having silicon-carbon linkages connecting the oxyalkylene moiety to the polysiloxane moiety, which surfactant is much more efficient in producing both flexible and rigid foams than are the prior art surfactants.
It is yet another aim of the present invention to provide an alkenoic acid polyether condensation product which can be used to add polyether groups to a polysiloxane by the use of an SiH-olefin addition reaction.
These and other objects of the present invention are accomplished by means of the invention set forth below.